Bone Remodeling Tutorial Notes | The University Of Western Ontario

University:
The University Of Western Ontario
Course:
ANAT 2200B | Systemic Anatomy of the Human Body
Academic year:

2022
Views:

321

Pages:

3
Author:

Kyuwon J.

Bone Remodelling ● Quiescence ○ resting phase ■ surface covered by lining cells ■ flattened and inactive osteoblasts ■ cell will make protective barriers to protect and prevent unnecessary resorption ● Resorption phase ○ Osteoclasts ■ multinucleated giant cells ■ derived from monocytes, macrophage recruited ■ tightly attaches to bone through sealing zones ● creates microenvironment, releases hydrochloric acids = dissolves hydroxyapatite crystal ● creates proteolytic enzymes ■ takes about 2-3 weeks ■ Forms Howship lacuna ● Reversal phase ○ pause in reabsorption, osteoclast will have apoptosis, will move away ○ reversal cell prepares for bone surface on new depositions ○ thin cement line is prepared. ■ Boundary between old and new bones ● Formation phase ○ osteoblasts recruited in cement lines ○ secretion of osteoid ■ non-mineralized bone matrix ■ rich in type 1 collagen, protein ○ withing 10-14 days osteoids will be mineralized in calcium and phosphates ○ Osteoblasts embedded in matrix (only some) ■ transformation into osteocytes (bone turnovers) ○ formation phase will happen between 3-4 months ● Quiescence (New Bone Formations) ○ surface in resting phases ○ osteoblast in actions ■ transforms in lining cells ■ Die by apoptosis ■ transforms (differentiates) to osteocytes ○ New bone structures units is established ■ osteons in compact bones ■ trabecula within spongy bone ● Regulation on Bone remodeling ○ Hormonal regulations ■ PTH ● stimulation on osteoclast activity ● indirectly through osteoblasts ■ Calcitonin ● inhibition of osteoclast activity ■ Vitamin D ● enhancing calcium absorption on bone mineralizations ■ Sex hormones ● inhibition of osteoclast ● stimulation of osteoblast = loss of estrogen after menopause => osteoporosis ■ Mechanical loadings ● Wolff’s Law ○ remodeling according ot mechanical stress applied to it ● Weight bearing stimulates osteoblast activity ○ Pathological regulations ■ excess glucocorticoids ■ immobilization ■ inflammatory cytokines => higher bone resorptions ● Time Course of Remodelling cycles ○ Cycle of 160-200 days ○ Resorption formations ■ bone loss ○ Formation > Resorptions ■ abnormal thickening